1. Field of the Invention
The present invention concerns a novel polyfunctional polymerization initiator and, more in particular, it relates to a polyfunctional polymerization initiator suitable to cationic ring-opening polymerization of heterocyclic monomers. The polymerization initiator according to the present invention can be utilized for obtaining telechelic polymer, block copolymer, comb-like or star-like polymer, etc. and it is, further, useful for the synthesis of crosslinker, coupling agent, IPN (interpenetrating network composite material), etc.
2. Description of the Prior Art
For cationic ring-polymerization of heterocyclic monomers, metal halides, alkyl halides such as methyl iodide and sulfonic acid esters such as methyl p-toluene sulfonate, etc., have been used. However, it is not possible with such monofunctional polymerization initiator to obtain telechelic polymer, block polymer such as A-B-A type polymer, comb-like or star-like polymer, etc. On the other hand, while it may be considered that telechelic polymer, block polymer comb-like or star-like polymer may be obtained by using a polyfunctional polymerization initiator such as alkyl dihalide or sulfonic acid diester, etc., the initiation is not fast and hence, polymers of controlled molecular weight can not be obtained by merely using a poly-substituted aliphatic compounds.
Further, as a technique for obtaining the telechelic polymer, block polymer, etc. as described above by the cationic ring-opening polymerization of heterocyclic monomers, there has been known a method of using a compound obtained by reacting a bisoxazoline and an ester as shown in the formula (1) as the polyfunctional polymerization initiator (Macromol., 19, 535 (1986)). ##STR1##
However, this method involves a problem that the polyfunctional polymerization initiator is difficult to be synthesized and the operations therefore are troublesome, as well as separation or purification of the products is difficult.
As another method, there has been known a method of using a poly-substituted aliphatic ester as shown in the formula (2) (Macromol., 20, 1729 (1987)). ##STR2##
In this method, however, since the rate of initiation reaction is lower than that of the propagation reaction, the initiator is present with on one or both of initiation groups remaining unreacted after the monomers have been consumed completely and, further, the molecular weight control of the polymer is difficult and the molecular weight distribution of the resultant polymer is broad.